This may sound obvious, but most rain eventually finds its way to the oceans, either via groundwater, rivers or lakes with permeable rock underneath. Some water, though, gets trapped in large basins that sit below sea level, and the water flows in but never flows out.
The Salton Sea near the Mexican border in Southern California has been at various levels for three million years. Technically a "saline lake," it is saltier than the ocean, though slightly less salty than the Great Salt Lake. The basin was nearly dry until the beginning of the 1900s when failed irrigation canals diverted the Colorado River into the large basin, and the raging river brought the snowmelt from the Rockies into the Salton Sea.
The engineers from the Southern Pacific railroad were unable to stem the waterfall that the river created. By petitioning Congress and President Roosevelt, the engineers received the "battleship" loads of rock they needed to block the hole, however, it took more than six months before they diverted the river again. The Salton Sea had grown larger than Lake Tahoe to its current size of about 15 miles wide and 35 miles long.
At first, it was unclear that this lake was a nuisance. The Sea was a productive fishery during the 40s, and with post-war wealth became a popular tourist spot in the 50s with resorts, beach-front homes, and water skiing.
But the incredible salinity of the lake and the heavy agriculture of Southern California slowly destroyed the ecosystem. Runoff from farms polluted the sea, and many of the fish species, save the hardy tilapia, could not survive, while migratory birds were poisoned with botulism and other lethal bacteria.
The State of California has been involved in efforts to restore the sea, but such extreme efforts are obviously easier said than done. In the interim the banks of the Salton Sea are a vivid, surreal empty landscape littered with dead fish and other detritus of human habitation.